Rafael Nadal of Spain addresses the media after announcing his withdrawal from the tournament due to a knee injury at the BNP Paribas Open in Indian Wells, Calif., on Saturday. Nadal was scheduled to play Roger Federer of Switzerland in the tournament semifinal. Photo by David Silpa/UPI | License Photo

Roger Federer of Switzerland addresses the media after receiving a walkover into the finals of the BNP Paribas Open in Indian Wells, Calif., on Saturday. Federer was scheduled to play Rafael Nadal of Spain, who was forced to withdraw due to a knee injury. Photo by David Silpa/UPI | License Photo

Roger Federer of Switzerland addresses fans after receiving a walkover into the finals of the BNP Paribas Open in Indian Wells, California on March 16, 2019. Federer was scheduled to play Rafael Nadal of Spain who was forced to withdraw due to a knee injury. Photo by David Silpa/UPI | License Photo

Roger Federer of Switzerland addresses fans after receiving a walkover into the finals of the BNP Paribas Open in Indian Wells, Calif., on Saturday. Federer was scheduled to play Rafael Nadal of Spain, who was forced to withdraw due to a knee injury. Photo by David Silpa/UPI | License Photo

March 16 (UPI) — Just hours before he was to take the court in the semifinals at the BNP Paribas Open in Indian Wells, California, Rafael Nadal was forced to withdraw due to a knee injury.

“I warm up today in the morning, and I felt that my knee was not enough good to compete at the level that I need to compete,” an upset Nadal said.